The present invention relates to a control apparatus for a motor that detects a magnetic pole position of a rotor and controls an AC motor without using a position sensor.
In order to control the speed and torque of an AC motor in high speed response, it is necessary to detect or estimate a magnetic pole position of a rotor. Various types of so-called magnetic pole position sensorless control systems that each detect a magnetic pole position of a rotor and control an AC motor without using any position sensor are proposed in recent years. Also among these systems, a system using an induced voltage which the AC motor generates, a system using an electrical potential difference equation of the AC motor, a system using the inductance characteristics of the AC motor, or the like is known as a magnetic pole position sensorless control system for a salient pole type AC motor.
For example, a magnetic pole position sensorless control system where two different magnetic pole position-estimating methods are combined is disclosed in U.S. Pat. No. 5,969,496 by Yamada et al. issued Oct. 19, 1999. This method tries the detection of a magnetic pole position by a first detection method that has a practical position detection precision, when a motor is rotating above a predetermined rotation speed. If position detection is not successful, this method detects a magnetic pole position by a second detection method that can perform position detection at under a predetermined rotation speed. Moreover, the rotation speed of the rotor of the motor is detected and one method is selected from the first and second detection methods according to the magnitude of this rotation speed.
Although the principles of two electrical angle detection methods are explained in the above-described conventional technique in detail. However, as for a switching method of two electrical angle detection methods, there is only the description of selecting one from between the first and second detection methods according to a state of a rotation speed. Before and after the switching of the two electrical angle detection methods, the phase difference between magnetic pole position estimates may arise, and torque change may arise in the motor. However, in the conventional technology, this point is not taken into consideration at all.
Moreover, in a conventional technology, an electrical angle is detected with the first detection method, which has a practical position detection precision at a predetermined rotation speed or faster, immediately after the startup of the motor. The rotation speed of the motor is obtained on the basis of a change of the electrical angle detected. However, immediately after the startup of the motor, when the rotation speed of the motor is below a predetermined rotation speed including the time of stopping, a rotation speed is obtained on the basis of a detected value of an electrical angle including an error. Hence the rotation speed obtained may include an error.
Moreover, in the conventional technology, control process routines of the motor are different at the time of the startup of the motor and at the time of usual operation. Hence the configuration of a control apparatus for the motor becomes complicated.
A typical object of the present invention is to provide a control apparatus for a motor that can estimate a rotor magnetic pole position of the motor in high speed response, high precision, and highly efficiency throughout the entire operating range of the motor.
Fundamental characteristics of the present invention are to estimate a rotor magnetic pole position of an AC motor with at least two different magnetic pole position-estimating methods, to switch at least two magnetic pole position-estimating methods according to an operating state of the AC motor throughout an operating range of the AC motor, and to estimate the rotor magnetic pole position of the AC motor.
One of at least two magnetic pole position-estimating methods is a carrier synchronization type estimating method of a magnetic pole position on the basis of a detected current value of the AC motor that is detected by synchronizing with a carrier of a PWM signal. Another method of at least two magnetic pole position-estimating methods is an equal potential type estimating method of a magnetic pole position on the basis of a detected current value of the AC motor detected in an equal potential state of the AC motor.
The carrier synchronization type magnetic pole position-estimating method is used in a low speed period including a startup period and a stop period of a motor, and the equal potential type magnetic pole position-estimating method is used for an AC motor at a middle and high speed. It is preferable to calculate a rotor magnetic pole position of the AC motor on the basis of an operating state of the AC motor in a predetermined period at the time of switching the a carrier synchronization type magnetic pole position-estimating method and the equal potential type magnetic pole position-estimating method. Alternatively, it is preferable to limit a variation amount of a rotor magnetic pole position of the AC motor estimated with the magnetic pole position-estimating method after switching on the basis of an operating state of the AC motor in a predetermined period. Alternatively, it is preferable to change the current detection timing of the AC motor. Alternatively, it is preferable to estimate a rotor magnetic pole position of the AC motor by using at least two magnetic pole position-estimating methods within a predetermined speed range of the AC motor.
Moreover, in the carrier synchronization type magnetic pole position-estimating method, it is preferable to discriminate whether the direction of a rotor magnetic pole position is the direction of a north pole or the direction of a south pole with estimating the direction of a rotor magnetic pole position of the AC motor at the time of the startup of the AC motor. The polarity discrimination of this rotor magnetic pole position can be performed on the basis of a variation amount of the motor current every fixed time that is generated by applying a predetermined amplitude of current in the estimated direction of the rotor magnetic pole position. Alternatively, the polarity discrimination can be performed on the basis of the detected current value of the AC motor detected in an equal potential state of the AC motor.
The present invention has at least two different magnetic pole position-estimating methods, and estimates a magnetic pole position of the AC motor by switching magnetic pole position-estimating means corresponding to each of a plurality of operating states of the AC motor. It is possible to estimate a magnetic pole position of the AC motor with the always-optimum magnetic pole position-estimating method.
Here, the followings are typical embodiments of the present invention.
A first form is a control apparatus for a motor that controls a voltage applied to an AC motor from a power converter by a PWM signal, the control apparatus for a motor which estimates a rotor magnetic pole position of the above-described AC motor with at least two different magnetic pole position-estimating methods, and estimates the rotor magnetic pole position of the above-described AC motor by switching the above-described at least two magnetic pole position-estimating methods according to an operating state of the above-described AC motor throughout an operating range of the above-described AC motor.
A second form is a control apparatus for a motor that controls a voltage applied to an AC motor from a power converter by a PWM signal, the control apparatus for a motor which estimates a rotor magnetic pole position of the above-described AC motor with a magnetic pole position-estimating method based on a detected current value of the above-described AC motor detected by at least synchronizing with a carrier of the above-described PWM signal, and a magnetic pole position-estimating method based on a current value of the above-described AC motor detected in a equal potential state of the above-described AC motor, and estimates a rotor magnetic pole position of the above-described AC motor with switching the above-described at least two magnetic pole position-estimating methods according to an operating state of the above-described AC motor throughout an operating range of the above-described AC motor.
A third form is a control apparatus for a motor that controls a voltage applied to an AC motor from a power converter by a PWM signal, the control apparatus for a motor which has: carrier synchronization type position-estimating means for estimating a rotor magnetic pole position of the above-described AC motor on the basis of a detected current value of the above-described AC motor detected by synchronizing with a carrier of the above-described PWM signal; equal potential type position-estimating means for estimating a rotor magnetic pole position of the above-described AC motor on the basis of a current value of the above-described AC motor detected in an equal potential state of the above-described AC motor; and means for switching magnetic pole position-estimating means from between the above-described carrier synchronization type position-estimating means and above-described equal potential type position-estimating means throughout an operating range of the above-described AC motor according to an operating state of the above-described AC motor.
A fourth form is a control apparatus for a motor that estimates a rotor magnetic pole position of an AC motor mounted in a vehicle, and controls the AC motor, the control apparatus for a motor which applies a signal for a rotor magnetic pole position estimation of the above-described AC motor to a control commander of the above-described AC motor in a low speed period including a startup period and a stop period of the above-described vehicle, inputs the current of the above-described AC motor, estimates a rotor magnetic pole position of the above-described AC motor by obtaining a current differential value by applying the above-described signal for an rotor magnetic pole position estimation, and estimates the rotor magnetic pole position of the above-described AC motor on the basis of an induced voltage of the above-described AC motor in a middle and high speed period of the above-described vehicle.
A fifth form is an electric vehicle having an AC motor which drives wheels, a vehicle-mounted power source, a power converter which converts into alternating current power the direct current power supplied from an on board power supply, and supplies the alternating current power to the above-described AC motor, and a control apparatus which controls the power converter, the electric vehicle where the above-described control apparatus is any one of the control apparatus described above.
A sixth form is an electric vehicle having an internal combustion engine which drives either of front or rear wheels, an AC motor which drives the other wheels, a vehicle-mounted power supply, a power converter which converts into alternating current power the direct current power supplied from the on board power supply, and supplies the alternating current power to the above-described AC motor, and a control apparatus which controls the power converter, the electric vehicle where the above-described control apparatus is any one of the control apparatuses described above.